Glycogen synthase kinase-3β (GSK3B) and cyclin-dependent kinase 5 (CDK5) are the 2 major protein kinases involved in abnormal phosphorylation of tau. To determine their potential role in the pathogenesis of Parkinson's disease (PD) we analyzed 2 functional single nucleotide polymorphisms (SNPs) of GSK3B (rs334558 and rs6438552) and rs735555 of CDK5 regulatory subunit 1 (CDK5R1) in 373 PD cases and 346 healthy controls of eastern India. The C,C and T,C haplotypes of GSK3B were respectively moderately associated with increased risk and protection for late onset PD (LOPD) (odds ratio [OR], 1.399; 95% confidence interval [CI], 1.069-1.829; p = 0.015, and OR, 0.436; 95% CI, 0.222-0.853; p = 0.016, respectively). Moreover, moderate to significant interaction between different loci were observed for the entire PD cohort or late onset PD only. However, among these interactions, individuals carrying the (C/C) genotype at both loci (rs6438552 and rs735555) had almost twice the risk of developing PD than those without this genotypic combination (OR, 1.871; 95% CI, 1.181-2.964; p = 0.009). Thus, synergistic effect between the 2 major tau kinases, through these SNPs, appears to determine the risk profile for PD.
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